Still image capturing devices are used to visually memorialize scenes, events, or items. Still image capturing devices, such as digital cameras, include a lens, a shutter, and an image sensor, such as film or an electronic image sensor. In addition, most modern cameras include a processor and/or other control electronics that function to control shutter speed, aperture, flash, focus, etc.
The shutter and the image sensor are the main components of a still digital image capturing device and operate together in order to produce a digital image. In operation, the shutter is opened briefly to expose the image sensor and thereby form an image. The operation of the shutter is very important, and the quality of the captured image depends on a proper exposure time based on lighting, movement of the subject, focus distance, etc.
The original prior art shutter approach was a mechanical shutter. The mechanical shutter has been widely used for a number of years and is generally in the form of an iris-type shutter. However, the prior art mechanical shutter has many drawbacks, including weight, large size, susceptibility to dirt and wear, and the difficulty of precisely controlling shutter exposure times over a wide range of conditions. In addition, the mechanical shutter exposes the entire image essentially at once (disregarding the difference in exposure durations between the center of the image and the edges in an iris-type mechanical shutter). The prior art mechanical shutter cannot independently vary the exposure duration of a region of the image.
In some prior art cameras, the mechanical shutter is electronically activated by a motor or other electrical actuator. This may produce a more accurate shutter control, but consumes a lot of electrical power, is inflexible, and still exposes the entire film at once and for an essentially constant duration.
The prior art cannot expose individual pixel elements or different pixel regions for varying times. Such capability may be desirable due to the fact that illumination of a subject is rarely uniform, except perhaps in a studio setting.
FIG. 1 shows an image 100 that is subdivided into regions A, B, and C. These regions may represent areas of differing image intensity. For example, region A may be a bright region, such as an area containing the sun in an outdoor scene, region B may be an area of a subject of medium light intensity such as a main subject of the image, and region C may be a darker foreground region. Region C may be the most difficult region to capture on an image, as the low light level may result in loss of image detail. In the prior art, these three regions are all treated equally, and are substantially uniformly exposed during an image capturing process. As a result, image capturing in the prior art often is less than satisfactory and may include regions of both over-exposure and under-exposure.
Therefore, there remains a need in the art for improvements in still image capturing devices.